1. Field of the Invention
The present invention relates to a liquid crystal display device. The invention particularly relates to a liquid crystal display device taking measures to prevent bright spots caused by scraped dusts of an alignment film.
2. Description of the Related Art
Liquid crystal display devices includes: a TFT substrate having pixel electrodes, thin film transistors (TFT), etc. formed in a matrix; a counter substrate disposed in facing relation to the TFT substrate and having color filters, etc. formed at portions corresponding to the pixel electrodes of the TFT substrate; and liquid crystals put between the TFT substrate and the counter substrate. Images are formed by controlling the light transmittance of liquid crystal molecules for each pixel.
In the liquid crystal display device, an alignment film is formed at the boundary between the counter substrate and the liquid crystal layer in the TFT substrate, and the alignment film is subjected to rubbing process or optical alignment process to put the liquid crystal molecules to initial alignment. Then, the amount of light transmitted through the liquid crystal layer is controlled by twisting or rotating the liquid crystal molecules by electric fields from the initial alignment state.
Meanwhile, to control the thickness of the liquid crystal layer, it is necessary to form spacers between the counter substrate and the TFT substrate. Conventionally, beads, etc. were dispersed as the spacers in the liquid crystal layer. In recent years, however, to accurately control the gap between the TFT substrate and the counter substrate more accurately, columnar spacers are formed on the counter substrate and the gap is controlled by the columnar spacers.
On the other hand, use of the columnar spacer raises a new problem. That is, when a pressure is exerted from the outside on the counter substrate or a temperature cycle is applied to the liquid crystal display panel, an alignment film present between the columnar spacer and the TFT substrate is scraped and scraped dusts cause bright spots.
JP-2009-282262-A describes a configuration in which the scraping of an alignment film by a columnar spacer is decreased by forming a pedestal having an area smaller than the area at the top end of the columnar spacer facing a TFT substrate and decreasing the thickness of the alignment film on the pedestal. JP-2009-282262-A describes a material and a process of decreasing the thickness of the alignment film on the pedestal, particularly, when an alignment film obtained by so-called optical alignment is used.
JP-2002-182220-A describes a configuration in which a columnar spacer having a groove is formed to a counter substrate and a portion of a large height and a portion of a small height are formed in one columnar spacer. Usually, the portion of large height defines a gap between the TFT substrate and the counter substrate. The portion of the large height deforms elastically when pressure is exerted from the outside to the counter substrate or the like, and a portion of the small height disperses the stress by being in contact with the TFT substrate thereby preventing buckling of the columnar spacer and enabling sooner recovery after removal of the pressure.
JP-2007-178652-A describes a configuration in which a spherical spacer is fixed to a counter substrate, a concave portion is formed to a TFT substrate at a portion in contact with the spherical spacer thereby enlarging a margin when the counter substrate and the TFT substrate are stuck together and preventing light leakage caused by displacement in stacking.